1. Field of the Invention
This invention relates to a stereomicroscope including an objective lens disposed opposite to an eye, and the first and the second observing optical systems for three-dimensionally observing the eye.
2. Prior Art of the Invention
Heretofore, a stereomicroscope used for a surgical operation, for example, an operation for cataracta and the like has been known.
The stereomicroscope of this type, as shown in FIG. 9, includes an objective lens 2 disposed opposite to an eye 1, the first and the second observing optical systems 3 and 4 for three-dimensionally observing the eye 1 through the objective lens 2, and an illuminating optical system 5 for illuminating the eye 1.
The first and second observing optical systems 3 and 4 comprises zoom lenses 6a and 6b, imaging lenses 7a and 7b, and oculars 8a and 8b, while the illuminating optical system 5 comprises an illuminating light source K, a condenser lens 9, and a mirror 10.
When the eye 1 is illuminated by the illuminating optical system 5, the eye 1 can be three-dimensionally observed at a predetermined magnification by operating the zoom lenses 6a and 6b.
By the way, an operation for cataract is performed in such a manner as to cut out the fore-brain of a crystal body and to take out turbidity. However, when the rest amount of turbidity becomes little, the turbidity is illuminated utilizing a reflected light on the eye fundus. The reason is that if a little amount turbidity is directly illuminated by the illuminating optical system 5, it becomes difficult to observe the turbidity.
However, when the optical axis 105a of the illuminating optical system 105 is different from the optical axis 104a of the observing optical system 104 as shown in FIG. 10 an illuminated area T1 by the illuminating optical system 105 on the eye fundus 1a is displaced from the spot O on the optical axis of the observing optical system 104 as shown in FIG. 11. And a reflected pencil of rays by the illuminated area T1 proceeds toward the illuminating optical system 105. As a result, when the crystal body 1b is observed from the observing optical system 104, the reflected light from the eye fundus 1a scarcely enters to the observing optical system 104, and a pupil area 1c is observed dark as shown in FIG. 12.
Therefore, when the crystal body 1b includes, for example, turbidities A and B, the turbidities A and B are not illuminated by reflected light from the eye fundus and observation of the turbidities A and B becomes difficult. In FIG. 11, the characters U, V, denote pencils of rays to be converged to the turbidities A and B by reflection from the eye fundus 1a. The symbolic character 1d in FIG. 12 denotes an iris.
When the illuminating optical system 105 is approached to the observing optical system 104 and the illuminated area T1 of the illuminating light reaches the spot O including a pencil of rays V as shown in FIG. 13, the peripheral pencil of rays including V among the reflected light by the illuminated area T1 in FIG. 13 enters the observing optical system 104. Owing to the foregoing, the pupil area 1c looked from the observing optical system 104, as shown in FIG. 14 is dark at an area G including the turbidity A and bright at an area Q including the turbidity B.
When the optical axis 105a of the illuminating optical system 105 and the optical axis 104a of the observing optical system 104 are aligned, the wost of the reflected pencil of rays by the illuminating area T1 shown in FIG. 15 enters the observing optical system 15. As a result, the pupil area 1c, when looked from the observing optical system 104, it comes to have a uniform brightness owing to the reflected light from the illuminated area T1 as shown in FIG. 16.
By the way, in the stereomicroscope shown in FIG. 9, since the optical path 5a of the illuminating optical system 5 is different from the optical paths 3s and 4s of the first and the second observing optical systems 3 and 4 on the objective lens 2, the pupil area 1c does not come to have a uniform brightness when the eye 1 is looked from the oculars 8a and 8b of the observing optical systems 3 and 4. That is, as is shown in FIG. 18, a left-hand side area P1 of the pupil area 1c becomes bright in a left view field L and the right-hand side area P2 becomes dark owing to inversion. In the right view field R, as is shown in FIG. 18, the right-hand side area P1 of the pupil area 1c becomes bright and the left-hand side area P2 becomes dark owing to inversion.
In this way, the position of the area P1 which becomes bright and the position of the area P2 which becomes dark in the pupil area 1c are different depending on the left view field L and the right view field R. Because of the foregoing, there arises such a problem as that image fusion of the pair of eyes becomes difficult to obtain and a surgical operation becomes very difficult to perform.
Also, there is another example of the prior art in which a half mirror H is installed as indicated by the broken line of FIG. 9 and the eye 1 is illuminated from an outside position Ha of the first and second observing optical paths 3a and 4a as shown in FIG. 19. However, this prior art does not provide a uniform brightness at the pupil area as in the above-mentioned example. That is, the area P1 which becomes bright and the area P2 which becomes dark in the pupil area 1c are different depending on the left view field L and the right view field R as shown in FIG. 20. Therefore, an image fusion of the pair of eyes becomes difficult to obtain and a surgical operation becomes difficult to performed.